The present invention relates to immunoglobulin E (IgE), IgE antagonists, anti-IgE antibodies capable of binding to human IgE, and to a method of improving polypeptides, including anti-IgE antibodies.
IgE is a member of the immunoglobulin family that mediates allergic responses such as asthma, food allergies, type 1 hypersensitivity and the familiar sinus inflammation suffered on a widespread basis. IgE is secreted by, and expressed on the surface of B-cells or B-lymphocytes. IgE binds to B-cells (as well as to monocytes, eosinophils and platelets) through its Fc region to a low affinity IgE receptor, known as Fc.epsilon.RII. Upon exposure of a mammal to an allergen, B-cells bearing a surface-bound IgE antibody specific for the antigen are "activated"0 and developed into IgE-secreting plasma cells. The resulting allergen-specific IgE then circulates through the bloodstream and becomes bound to the surface of mast cells in tissues and basophils in the blood, through the high affinity receptor also known as Fc.epsilon.RI. The mast cells and basophils thereby become sensitized for the allergen. Subsequent exposure to the allergen causes a cross linking of the basophilic and mast cellular Fc.epsilon.RI which results in a release of histamine, leukotrienes and platelet activating factors, eosinophil and neutrophil chemotactic factors and the cytokines IL-3, IL-4, IL-5 and GM-CSF which are responsible for clinical hypersensitivity and anaphylaxis.
The pathological condition hypersensitivity is characterized by an excessive immune response to (an) allergen(s) resulting in gross tissue changes if the allergen is present in relatively large amounts or if the humoral and cellular immune state is at a heightened level.
Physiological changes in anaphylactic hypersensitivity can include intense constriction of the bronchioles and bronchi of the lungs, contraction of smooth muscle and dilation of capillaries. Predisposition to this condition, however, appears to result from an interaction between genetic and environmental factors. Common environmental allergens which induce anaphylactic hypersensitivity are found in pollen, foods, house dust mites, animal danders, fungal spores and insect venoms. Atopic allergy is associated with anaphylactic hypersensitivity and includes the disorders, e.g., asthma, allergic rhinitis and conjunctivitis (hay fever), eczema, urticaria and food allergies. However anaphylactic shock, a dangerous life-threatening condition anaphylaxis is usually provoked by insect stings or parental medication.
Recently, a treatment strategy has been pursued for Type 1 hypersensitivity or anaphylactic hypersensitivity which attempts to block IgE from binding to the high-affinity receptor (Fc.epsilon.RI) found on basophils and mast cells, and thereby prevent the release of histamine and other anaphylactic factors resulting in the pathological condition.
Applicants' copending application U.S. Ser. No. 08/232,539, filed Apr. 21, 1994 describe human IgE/IgG1 chimeras wherein IgG1 residues are substituted for the analogous IgE residues. Applicants' copending application U.S. Ser. No. 08/405,617 describes humanized anti-IgE antibodies wherein a murine antibody directed against human IgE (MaE11) was used to provide the CDR regions which were substituted into an IgG1 immunoglobulin framework (rhuMaE25). A technique of humanization is described in Reichman, L. et al., (1988) Nature 332: 323 and in Jones, P. T. et al. (1986), Nature 321: 522.
While humanization of murine antibodies has been established to provide anti-IgE molecules which provide similar affinity to IgE as murine MaE1 without the immunogenic response elicited by the latter (Shields et al., (1995) Int. Arch. Allergy Immunol. 107: 308-312), it has still not resulted in the construction of an anti-IgE with affinity for IgE which is decidedly better than MaE11 or a murine anti-IgE.
Recombinant monoclonal antibodies are subject to degradation reactions that affect all polypeptides or proteins, such as isomerization of aspartic acid and asparagine residues. As shown the reaction scheme below, aspartate residues (I) in -Asp-Gly- sequences can isomerize to isoaspartate (III) through a cyclic imide intermediate (II). (Geiger & Clarke, J. Biol. Chem. 262: 785-794 (1987)). The carboxylic acid side chain of the aspartic acid (I) reacts with the amide nitrogen of the adjacent glycine to form a cyclic aspartic acid intermediate (II) which then forms into an -isoaspartic acid-glycine- residue(III). The equilibrium, rate, and pH dependence of this reaction have been studied in model peptides separated by reversed phase high performance liquid chromatography. (Oliyai & Borchardt, Pharm Res. 10, 95-102 (1993)). The tendency to undergo isomerization is believed to also depend upon the local flexibility of the portion of the molecule containing the -Asp-Gly-sequence (Geiger & Clarke, supra). ##STR1##
An example of a known antibody which undergoes aspartic acid isomerization is the potent anti-IgE antibody known as rhuMabE-25 (E-25). This event may occur spontaneously, but can be induced to occur when E-25 is incubated at 37.degree. C. for 21 days. The end result is the insertion of an additional methyl group into the polypeptide backbone of the antibody, which can result in conformational changes and reduction in binding affinity. A study of E-25 with -c-Asp-Gly- and -iso-Asp-Gly- variants at position VL 32-33 indicated that while the isomerization event can be minimized by substitution of alanine or glutamic acid for residue VL32, the substitution itself results in a three-fold reduction in binding. Cacia et al., supra.
Thus, there exists a great need for the creation of improved polypeptides, including antibodies, which not only don't exhibit the "deactivating" event of aspartyl isomerization, but also display affinity to the target molecule (e.g., antigen) equal to or greater than the unimproved polypeptide's affinity.